The block etheramides of the invention, such as the polyetherpolyamides described in DE-PS 30 06 961 or the polyetheresteramide block copolymers (polyetheresteramides) described in DE-PS 25 23 991, belong to the category of polyamide elastomers (PA-elastomers). The term "block copolyetheresteretheramide" emphasizes that the polyether contents of the products according to the invention are linked to the polyamide segments by ester or amide bonds. For the sake of simplicity, the term "PA-elastomers" will be used herein.
The most important PA-elastomers found in the market nowadays undoubtedly include those whose polyamide segments --CO--D--CO-- had resulted from the polymerization or the polycondensation of caprolactam, laurolactam, or the corresponding .omega.-amino-.alpha.-carboxylic acids in the presence of a dicarboxylic acid.
According to DE-PS 25 23 991, PA-segments having terminal carboxyl groups are esterified with .alpha., .omega.-dihydroxypolyethers and the polyetheresteramides are thus obtained. According to DE-PS 30 06 961, PA-segments are reacted with .alpha., .omega.-diamino polyethers to form polyetheramides. Both methods of synthesis of PA-elastomers are subject to a number of restrictions; hence, a highly flexible PA-6-elastomer having a flexural modulus of elasticity of less than about 200 N/mm.sup.2 (measured in the dry state) and acceptable properties for processing and use cannot be produced by the batch processes according to the teachings of either of these references.
DE-PS 25 23 991 describes various linear or branched aliphatic polyoxyalkylene glycols as components which have a flexibilizing effect, in particular the following:
I: Polyoxyethylene glycol=.alpha., .omega.-dihydroxypoly-(oxyethylene). PA0 II: Polyoxypropylene glycol=.alpha., .omega.-dihydroxypoly (oxy-1,2propylene), PA0 III: Polyoxytetramethylene=.alpha., .omega.-dihydroxypoly-glycol (oxytetramethylene), PA0 IV: Copolyethylene glycol-propylene glycol PA0 V: .alpha., .omega.-diamino-poly-(oxy-1,2-propylene) or PA0 VI: .alpha., .omega.-bis-3-aminopropyl-poly-(oxytetramethylene),
Although highly flexible products can be produced with component I, they have the distinct disadvantage that they absorb considerable quantities of water when in contact with moisture. Thus, with 50% by weight of segments of I, the water absorption corresponds approximately to the weight of the respective block polymer.
Polyoxypropylene glycol (II) can, if its average molar mass exceeds the value of 1000 required for highly flexible, readily processable PA-6-elastomers, be mixed only to a limited extent with the respective short-chain, carboxyl-terminated PA-6-segments (Mn .gtoreq.1300), so a high molecular weight polymer cannot be built up. A further distinct disadvantage, at least for batchwise production processes, is that polyoxypropylene glycol is very sensitive to elevated temperatures and tends to discolor and decompose under the normal polycondensation conditions. In addition, it can only be esterified with difficulty due to its individual secondary alcohol function.
Polyoxytetramethylene glycol (III) is poorly miscible with PA-6-segments, which limits the potential polymers to less flexible products. The drawbacks mentioned with regard to I and II also apply to IV.
According to the teaching of DE-OS 30 06 961, PA-6-elastomers can be produced by condensation of PA-6 containing terminal carboxyl groups with
wherein an industrial, hydrogenated or non-hydrogenated, dimerized fatty acid or "dimeric acid" containing 36 carbon atoms (which can contain a small quantity of trimerised fatty acid containing 54 carbon atoms) is preferably used as a chain length regulator.
It is just as impossible to produce a highly flexible PA-6-elastomer using the flexibilizing component V as with component II which is comparable therewith. This is due to the limited miscibility of PA-6-segments (Mn.gtoreq.1300) with the respective poly-(oxy-1,2-propylene)-segments. However, the thermal stability of diamine V is significantly higher than that of diol II. Its reactivity toward carboxyl groups is greater than that of diol II.
The use of component VI for producing a highly flexible PA-6-elastomer is hindered by its poor miscibility with the PA-segments. In addition, the diaminopolyether VI is so expensive (due to its complicated synthesis) that it cannot be considered for the commercial production of a highly flexible PA-6- or PA-12-elastomer.
According to the teaching of DE-PS 30 06 961, a satisfactory result cannot be achieved either with the polyether component V containing terminal amino groups or with VI for the synthesis of a highly flexible PA-12-elastomer. Polyetherdiamine VI fails for the above-mentioned reason and with diamine V, having contents of more than about 30% by weight in the PA-12-elastomer, only products which have yellow to brown discoloration and are sometimes markedly decomposed can be produced.
If a PA-12 containing terminal carboxyl groups is polycondensed with the above-mentioned components I to IV according to DE-PS 25 23 991, then the disadvantages already mentioned with regard to I, II or IV also apply. With III as flexibilizing component, PA-12-elastomers of almost any flexibility having very good properties for processing and use can generally be produced. However, these PA-12-elastomers still have the following distinct disadvantages.
The first disadvantage resides in the inadequate compatibility of PA-12-segments having an average molar mass higher than about 1000 and segments of the flexibilizing component III having an average molar mass higher than about 1100 in highly flexible elastomers having a content of III amounting to more than about 45% by weight. The lack of compatibility is revealed by the cloudy milky appearance of the PA-12-elastomers in the solidified (crystallized out) state; the strength of parts produced therefrom is diminished transversely to the processing direction owing to the delaminability of the layered structures. The increased susceptibility to mechanical wear, for example, the abrasion of such PA-12-elastomer products, is closely related. The above-mentioned disadvantages cannot be eliminated by modifying the production process.
The second disadvantage of these PA-12-elastomers is that they are not unreservedly suitable for coinjection molding or injection welding. The latter process is a special injection molding process in which polymer A is injected in a conventional injection mold onto a solidified part of the same--or usually a different--polymer inserted therein. Finished articles of which the functions can be optimally adapted to the specific requirements by suitable polymer combinations are obtained in this way. For example, it is possible by this process to restrict the elasticity in a given finished article to the regions where it is actually advantageous and to keep the remainder of the article rigid. The process also affords considerable advantages in the coloring of injection moldings.
The fundamental condition for the application of injection welding to a specific pair of polymers is good adhesive strength at the contact faces between the polymers. High strength interlayer adhesion is achieved because the injection molded polymer melts a thin layer of the inserted plastic part and the melts of the two materials are mixed together. The miscibility of the polymers must be ensured; obviously, the process fails if the polymers are incompatible.
With regard to PA-12-elastomers with co-component III according to DE-PS-25 23 991, they are preferably combined with other elastomers of this type or with unmodified PA-12. The adhesive strength achieved in these cases is generally good, but it does not meet all requirements, particularly if the molecular weight of the PA-12-elastomer is comparatively low.
The production of good adhesive strength is difficult at relative viscosities (as a measure of the molecular weight of the PA-12-elastomers) of less than 2.1 (measured as 0.5% solution in m-cresol at 25.degree. C. according to DIN 53727).